Systems and methods for separating soft burned and hard burned calcium oxide

ABSTRACT

Systems and methods to effectively sort calcined lime (quicklime) particles to produce products with more consistent size and burn time characteristics after the quicklime particles have been created and without the use of specialized additives. Specifically, such systems and methods sort the quicklime particles below a selected size into a softer burned and harder burned fraction based on their size. The fractions are burned in the kiln together and as a singular product, but can be classified from each other after calcining.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a Continuation of U.S. Utility patent applicationSer. No. 15/144,258 filed May 2, 2016, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/155,923, filed May 1, 2015.The entire disclosure of all the above documents is herein incorporatedby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This disclosure is related to the field of quicklime production andproducts, specifically to segregation of quicklime (calcium oxide) intocompositions which are soft burned versus those that are hard burned inthe calcining process.

2. Description of the Related Art

Calcium oxide, which is commonly referred to as quicklime (or even justlime), is an incredibly useful compound with a storied history in avariety of industrial applications in all sorts of areas. These usesrange from many years ago where it was heated to produce stage lighting(where the term “lime light” comes from) and as a building mortar forstone structures, to more modern uses where it is an essential componentof building materials such as cement, concrete, and plaster.

Outside of the most common construction uses, quicklime is explosivelyreactive to water, which can make it dangerous to handle or to beexposed to and is even believed to have been weaponized in the ancientworld. However, quicklime's fast reaction time with certain chemicalsalso makes it very useful as a part of a large number of industrialchemical processes and operations such as gas scrubbing, biofuelrefining, and rubber manufacture, where quicklime can be used to carryout a particular reaction quickly. In these types of processes, thequicklime is commonly used as a reactant or as a catalyst. While many ofthese processes have the simple requirement that faster reacting isbetter, it is often more important that the reactivity of quicklime beknown and consistent, than that it be particularly fast or slow.

If the quicklime is not sufficiently reactive (low reactive), it canremain in an unreacted form after the reaction to which it is connectedis completed. This can result in the quicklime being a contaminant orwaste product in the result. If it is too reactive, it is also possiblethat the quicklime can have undesired effects on the process due to itreacting too quickly or reacting with products (such as surrounding air)instead of as part of the desired reaction. In both scenarios, it isoften the case that the person interested in having the reactionperformed has to use an excessive amount of the quicklime to get theresult they want, and that can become expensive.

One concern in the production of calcium oxide is that chemical analysisof the oxide is often insufficient to determine if it meets all theneeds of the various process into which it is to be used. Basically,because the calcium oxide is being used in a chemical reaction process,one would presume that calcium oxide products that are chemicallysimilar should perform identically. However, it has been found thatsometimes the physical properties (reactivity, particle sizedistribution, surface area, pore volume, etc.) of the calcium oxide haveactually proven more important to its performance in the chemicalreaction process. In many cases, this can be intuitive. For example, thesame mass of a calcium oxide which has been pulverized to a smaller sizeis generally expected to have more surface area (per unit mass) than alarger particle sized counterpart. Thus, for reaction activities wheresurface area is relevant, a greater surface area composition wouldpresumably work better regardless of similarity of chemical composition.

It is believed that there are numerous important properties in calciumoxide that have no relation to chemical analysis. There are numerouschanges in the physical structure of the resultant lime that appear tobe a direct result of the conditions under which the limestone wassubjected to during the thermal decomposition (calcination) process thatformed the quicklime from raw limestone (calcium carbonate or CaCO₃).Further, these changes can result in quicklime products with a varietyof different reactivity and uses.

Lime calcination generally is performed in some form of lime kiln. Thereare a large number of different types of lime kiln designs available inmodern calcium oxide production. Some designs are little changed fromprocesses used hundreds of years ago, while others are of relativelymodern design. While there are a huge number of different kilns, mostindustrial processes use only a relatively small number of differentdesigns and the designs are often selected based on desired output, andavailable input, as certain types of kilns are better for producingcalcium oxide with certain qualities and characteristics, and foroperating on certain kinds of limestone feed stocks.

Regardless of the design, kilns are generally focused on two main typesof operation, rotary or vertical shaft, and utilize a continuous inflowof limestone and outflow of calcium oxide. The systems are traditionallycharacterized by providing a counter-current flow of solids and gasesand usually utilize three stages of action in the lime burning process.The first stage is a preheating zone where the feed stock limestone isheated to a temperature generally above 800° C. by exposure to escapingexhaust gases from actions later in the structure. In the calciningzone, the limestone is heated to above 900° C. (and commonly 1000° C.)to cause the calcination. The resultant calcium oxide (quicklime) isthen cooled in the third zone to prepare the quicklime for removal fromthe kiln. This is discussed in more detail in documents such as thoseavailable at www.roadbondsoil.

In the lime calcination process, differences in resultant physicalproduct have generally been linked to the specific temperature to whichthe source limestone is exposed in the calcining zone and to thespecific particulate qualities of the limestone. In theory (which isbasically operation under idealized conditions), during the calcinationprocess, the applied heat causes so great of a molecular activity in theatoms making up the molecules of limestone (CaCO₃) that the CO₃ ion isbroken up. The CO₂ molecules escape as a gas, while the remaining oxygenatom becomes the appropriate part of the CaO structure. The action ofthe CO₂ egress from the molecule creates a hole or “pore” in the surfaceof the quicklime particle. The size of this hole then serves to increasethe surface area of the particle, which can assist in the reactivityspeed of the quicklime.

While the theory is well understood and appears sound, the practicalenvironment inside a lime kiln can disagree with the theory. In thefirst instance, the limestone feed into a lime kiln is not of consistentsize. It is near impossible to generate any form of particulate productwith a uniform particle size. Instead, particles, such as feedlimestone, are generally crushed or pulverized to a particle sizedistribution that is within certain parameters acceptable to thespecific kiln and desired output. This means that the feedstocklimestone includes a majority of particles within a certain, oftenfairly narrow, size band, but will also still include a number ofparticles both smaller and larger than the band.

The feed stock also can include a number of impurities (materials whichare not limestone) of a variety of sizes and chemical compositions.These can also alter the calcining process due to these impurities notbeing part of the calcining reaction and potentially interfering withthe process. Further, the impurities' presence (or not) can alsoactually alter the physical characteristics of the limestone componentof the feed. For example, if an impurity is particularly hard,pulverizing a mixed feed of limestone and a large amount of the impurityto a narrow band may actually result in the limestone portion of thecomposition being only in the smaller part of the band and having anarrower distribution, while the exact same process and an output withidentical physical distribution, but less of the impurity, can result ina wider band of the limestone particle distribution.

Further, in order to provide for operating efficiency, conservation ofheating fuel, and reduced combustion emissions, most lime kilns, reuseheated air from one stage of the process to another. Thus, air heated bythe cooling quicklime in the cooling zone is used as preheated air forthe calcining zone. Further, the exhaust air from the calcining zone,generally including the released CO₂ from the calcining process, is usedas the preheating air in the preheating zone. While this generally makesthe kiln more energy efficient, it should be clear that it can makeexact temperature control in each zone fairly complex. As the calciningprocess is generally a continuous operation, the temperature willgenerally fluctuate within the calcining zone (as well as the otherzones) depending on the specific parameters of the process at anyinstant and with simple movement of heat currents inside the kiln.

It should be apparent from the above description that taking intoaccount the variability of limestone particle sizes and compositionalong with the variability of specific heat within a zone (both globallyin the zone, and due to specific heat currents moving through the zone),it is very difficult to produce an ideally consistent quicklime product,particularly from two feed-stocks sourced from different geographiclocations.

If a particle is exposed to too little heat (or is too big), the core ofthe limestone can remain calcium carbonate and only the outside convertsto calcium oxide. This is commonly referred to as an output which is“rocky.” Alternatively, overexposure to heat can result in the limelosing reactivity. Specifically, if the lime is exposed to sufficientheat, the surface can vitrify, which can make it less reactive as it ishard for water to penetrate the hard surface. Lime which has beendesirably burned for high reactivity is often referred to as “softburned” while that which has been exposed to a greater amount of heat isoften referred to as “hard burned” or “dead burned” if exposed to anexcessive amount of heat. Between hard and soft is “medium burned”.

Classification of quicklime into the various categories is often basedon the ASTM C-110 standard which provides for the degree rise intemperature in 30 seconds and 180 seconds (referred to as R30 and R180)for the quicklime in a hydration reaction. Soft burned lime is generallyclassified as that which has an R30 of 15 degrees or greater, mediumburned lime is typically around 13-14 degrees, and hard burned lime isgenerally less than that. Similarly, a soft burned lime typically has aR180 of greater than 40 degrees, a medium burned lime has an R180 of 30to 40 degrees, and a hard burned lime has an R180 of less than 30degrees. Rocky quicklime is generally incompletely reacted and can beclassified on that ground instead of using R30 or R180 values.

Because of the variations in limestone particle size and the unevennature of most heating, the quicklime produced by most lime kilns, likethe limestone product that goes in, is generally produced as aparticulate with a number of distributions related to particle size,burn time, and a variety of other factors. The output of a kiln isroutinely pulverized prior to classification, and this “kiln discharge”has been found to have a relatively broad distribution of particleburns. Further, the kiln discharge can vary heavily throughout runs dueto variation in inputs as well as heat changes. Consecutive runs canoften see swings of 2-3 times as much production of hard vs. soft burnedmaterial, even with relatively consistent input streams.

Because the output has a wide variety of burn levels, applications towhich the quicklime is put have to deal with some level of deviationfrom their ideal rate. That is, the process for the quicklime must bedesigned to accept that some of the particles in the distributionprovided, regardless of how well it is manufactured, may be burnedinsufficiently (rocky) while still others will be hard burned. If thatcauses changes in the reaction, or results in impurities in theresultant material, the manufacturing process has to take such thingsinto account and will generally produce an end product that is within arange of acceptable impurities from imperfectly reacted quicklime. Itshould be apparent that this range is generally a middle ground as goingtoo far one direction or another can create new problems.

In certain applications, however, it is desirable to utilize only softburned lime, while in other processes, hard burned lime is desired and,in still other processes, medium burned lime is desirable. For example,in hydration reactions, quicklime as a particle scrubber in flue gases,or propionate or rubber formation reactions, faster reaction times (andthus soft burned quicklime) are generally desired. Alternatively, inapplications such as the generation of autoclave (aerated) concrete orfor food additives, a medium burn of quicklime is often desired because,if these reactions are too fast or too slow, a less desirable productcan be produced. Finally, in applications such as moisture scrubbers orfor detergent additives for petroleum products, hard burned lime isgenerally desirable, as a slow reaction is desired to prevent potentialdangers and to provide stability.

Regardless of the type of quicklime desired for an application, it hasbeen generally considered cost-prohibitive to try and segregatequicklime by the degree of burn in the kiln discharge. Methods such asmanual or automatic optical sorting of kiln discharge can provide for amore consistent quicklime product (e.g., soft, medium, or hard burned),but can be very expensive to implement and, therefore, raw output isoften classified as a single product based on where it “better” falls.In most cases, this makes the end product a medium burned product, eventhough the product will include a not insubstantial amount of soft andhard burned product. It would not be surprising for a medium burnedproduct to actually only have 30-40% of its particles actually be mediumburned particles, but to then have a distribution of particles that arehard and soft burned as well. The distribution of these will oftendepend on if a more or less reactive product is easier to use.

Instead of sorting quicklime particles after they are produced, in orderto produce more particular products (e.g., those that are moreconsistently soft or hard burned), the inputs are generally more rigidlycontrolled, or kiln operating parameters are altered, to produceparticular end products. To better control the variables, improvedfeedback loops are often provided to more accurately monitor and adjusttemperatures in real time. Further, limestone may be processed inparticularly sized batches or load speeds to provide for more consistentcontrol or at least trend the output in a particular direction. Forexample, if hard burned product is more desirable, internal temperatureand residence time for the lime can be increased, or smaller limestoneinputs can be provided. Alternatively, if soft burned product is moredesirable, more exacting control of temperature in the calcining zonemay be implemented and the residence time of the limestone input in thekiln can be reduced.

Still further, limestone inputs may be much more processed, screened,and evaluated prior to the kiln to provide for a more uniformly sizedfeedstock where particular burn outcomes are desired. In this way, theinput particle size distribution is narrower. Thus, residence times andheat set for a median particle size are more likely to not result in asubstantial difference in properties for a large number of the particlespresent. While any of these methods can prove effective at producing amore consistent quicklime that has a narrower size band and a higherprobability of particles with a particular burn profile, they generallyalso impose substantial additional costs on the production due toinherent inefficiency (from increased control and processing). Kilns arealso expensive and, in certain types of kilns, a higher calcinationtemperature combined with a shorter burn time coupled with issues likeuneven heat distribution and inconsistent limestone/quicklime movementin the kiln can simply not be controlled enough to provide a consistentquality quicklime output. Thus, control of inputs is often limited tovery particular, and commonly expensive, quicklime products.

Because of all the above problems, a variety of solutions have beenproposed which provide for better control of the reaction time of thequicklime without altering the characteristics of the quicklime. Inparticular, the use of additives of various types in the resulting limereaction allows for the reactivity of the lime to be controlledexternally. Patents such as U.S. Pat. Nos. 6,395,205 and 4,464,353, theentire disclosures of which are herein incorporated by reference, aredirected to certain additives to control the speeds of certain types oflime reactions. Further, U.S. Pat. No. 5,616,283, the entire disclosureof which is herein incorporated by reference, is directed to an additiveto control viscosity of a hydrated lime. Notably, viscosity is aproperty that has been an issue in certain commercial reactions and isrelated to the burn characteristics of the lime.

SUMMARY OF THE INVENTION

The following is a summary of the invention, which should provide to thereader a basic understanding of some aspects of the invention. Thissummary is not intended to identify critical elements of the inventionor in any way to delineate the scope of the invention. The sole purposeof this summary is to present in simplified text some aspects of theinvention as a prelude to the more detailed description presented below.

Because of these and other problems in the art, there is a need forsystems and methods to effectively sort quicklime particles to produceproducts with more consistent size and burn time characteristics afterthe quicklime particles have been created without the use of additives.Specifically, such systems and methods would preferably allow forcalcined lime (quicklime) to be sorted into softer burned and harderburned fractions after the fractions are burned in the kiln together.

There are described herein among other things, systems and methods forseparating soft burned quicklime from hard burned quicklime, one suchmethod comprising: grinding a limestone feedstock including limestoneand impurities to a first size; calcining said limestone in saidlimestone feedstock to produce a quicklime; milling said quicklime intoa quicklime particulate, said quicklime particulate having between about80% and about 90% of its particles smaller than 100 mesh; separatingsaid quicklime particles which are smaller than 100 mesh from aremainder which is larger than 100 mesh, said quicklime particles whichare smaller than 100 mesh having a size distribution with two peaks in abimodal distribution; and running said quicklime particles which aresmaller than 100 mesh through a classifier to separate said quicklimeparticles which are smaller than 100 mesh into a soft burned and a hardburned fraction separated by a dividing point, said soft burned fractionbeing particles smaller than said dividing point and said hard burnedfraction being particles larger than said dividing point; wherein saiddividing point is between said two peaks in said bimodal distribution.

In an embodiment of the method, the dividing point is defined by aspecific particle size which may be between about 4 and about 7 microns.

In an embodiment of the method, the dividing point is defined as a sizeunder which a percentage of particles in said remainder is below, whichpercentage may be 20%.

In an embodiment of the method, the soft burned fraction has an R180 ofgreater than 40 degrees.

In an embodiment of the method, the hard burned fraction has an R180 ofless than 30 degrees.

In an embodiment, the method further comprises: grinding said remainderto a size which is smaller than 100 mesh; and classifying said groundremainder as a very hard burned fraction.

In an embodiment, the method further comprises: selecting a seconddividing point; and removing from said soft burned fraction a mediumburned fraction, said medium burned fraction being particles larger thansaid second dividing point. The soft burned fraction may have an R180 ofgreater than 40 degrees, said medium burned fraction may have an R180between 30 and 40 degrees, and said hard burned fraction may have anR180 of less than 30 degrees.

In an embodiment, the method further comprises: selecting a seconddividing point; and removing from said hard burned fraction a mediumburned fraction, said medium burned fraction being particles smallerthan said second dividing point. The soft burned fraction may have anR180 of greater than 40 degrees, said medium burned fraction may have anR180 between 30 and 40 degrees, and said hard burned fraction may havean R180 of less than 30 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a particle size distribution of an embodiment of a rawquicklime kiln discharge pulverized to approximately 80-90% passing a100 mesh screen.

FIG. 2 depicts a particle size distribution of an embodiment of thecoarse component of the distribution of FIG. 1 . In this embodiment, thecoarse component was selected as the coarsest about 80% of the rawoutput. Specifically, it was the coarsest 78.3% of the output.

FIG. 3 depicts a particle size distribution of an embodiment of the finecomponent of the distribution of FIG. 1 . In this embodiment, the coarsecomponent was selected as the finest about 20% of the raw output.Specifically, it was the finest 21.7% of the output.

FIG. 4 depicts the reaction characteristics of the raw lime, and each ofthe fractions of FIGS. 2 and 3 . Reactivity is shown based on specificsof reacting the various compositions with water in slaking. The particlesize distributions are also provided numerically, and the BET surfacearea and pore volume for the various compositions are also provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Hard burned lime is generally believed to be created because “pores”created in the particle due to the CO2 gas escaping close. Thus, thesurface becomes impervious as there is no point at which anothermolecule can enter. With the CO2 removal and the molecular re-alignmentin the calcining zone, the void space created in a very soft burned,un-shrunken, lime particle can be around 56% of the total volume. As thelime is subjected to higher calcination temperatures, theinterconnecting voids and open pores between the CaO crystals begin toshrink.

In a soft burned lime, it is also believed that the individual CaOcrystals are loosely packed and joined only by point contact. Withincreasing heat, the point contact between crystals becomes more of asurface-to-surface contact. The initial small crystals formed in softburning begin to grow at the expense of adjacent particles, gettinglarger and more firmly bound. The compressive strength of lime, andtherefore the resistance to breakage, is greatly affected by the crystalre-alignment and growth. Soft burned lime with loosely joined crystalsgenerally has a low compressive strength, while a hard burned lime withthe larger firmly bound consolidated crystals (agglomerates) is veryresistive to breakage.

This difference in compressive strength can be used to categorize limein a novel fashion. Once quicklime has been produced by a kiln, thequicklime is often pulverized to produce a kiln discharge lime with aparticular size distribution. Because of the compressive strengthdifference between lime types, it has been found that it is possible tofirst pulverize the raw quicklime output and then use air classificationor other separation technology to separate the quicklime into at leasttwo fractions. Depending on the embodiment, the fractions may classifythe lime where particles are either above or below a certain size, orwhere a certain percentage of the raw lime is provided into a certainfraction. Such size classification has been found to produce a finefraction that is dominated by soft burned particles, and a coarsefraction dominated by hard burned particles. This allows for bothfractions to have improved usefulness over their original mixture.Further, a middle fraction can also be produced which is dominated bymiddle burned lime in a still further embodiment. Being able to providefor a quicklime product which is dominated (e.g., a vast majority ofparticles meet that criteria) by a particular type of burn allows forspecialty products to be provided from any lime discharge without asmuch control of the inputs. Thus, lime products can be provided whichprovide particular reaction characteristics, and or relatedcharacteristics such as hydrate viscosity.

In an embodiment of the systems and methods, the raw quicklime is firstground to a fineness of around 80-90% minus 100 mesh. This can allow forremoval of impurities and other particularly large particles initially.Particles above 100 mesh (10-20% generally) is removed and generallyprovides a very hard burned product and a relatively large particlesize. The particles are generally too big for commercial applications,but this product can be further crushed separately to remove impuritiesand to produce a very hard burned quicklime or even dead burnedquicklime of desirable size.

The remaining 80-90% that passed the 100 mesh filter is processedthrough an air classification system or other separation technology thatserves to separate the particulate into at least two fractions.Generally, two fractions will be used. A coarse fraction will comprise agreater percentage of larger agglomerates and heavier hard burned limewhich is separated from the fine fraction which comprises a greaterpercentage of softer smaller agglomerates, and lighter soft burnedquicklime. The finer fraction, which comprise a much higher percentageof soft burned lime, can be provided as a far more reactive product,while the coarser fraction, which tends to include a greater percentageof hard burned lime and larger agglomerates, can be used in applicationswhere greater compressive strength, or less reactivity, is desired. Inan alternative embodiment, three factions may be used to provide amedium burned center fraction.

The results of an exemplary separation of an above 100 mesh fraction,and then a separation of the particles below 100 mesh into twofractions, are shown in the FIGS. FIG. 1 shows the particle sizedistribution of raw quicklime particles after they are removed from akiln (kiln discharge), pulverized, and categorized to remove particlesabove 100 mesh. As can be seen in FIG. 1 , there is a relatively broaddistribution of particles in the below 100 mesh fraction indicating thatthe raw kiln discharge is not particularly well suited for eitherapplications for soft burned or hard burned lime. It should also benoted that the distribution is slightly bimodal with two possible peaks.These two peaks can be separated and in FIG. 2 , the distribution of thecoarse (hard burned) peak fraction is shown, while in FIG. 3 thedistribution of the fine (soft burned) peak fraction is shown.

It should be recognized that the specific cutoff between the coarse andfine fractions will generally depend on the specific preference for softvs. hard burned lime, desired reaction times or reactivity, and othercharacteristics of the lime dictated by the resultant use to which it isto be put. Higher separation points will generally allow for more hardburned lime to be present in the fine fraction, but will allow for moreof the resultant quicklime to be provided as part of the fine fractionand can be used to select particular reaction times for processes wherepure reactivity is not necessarily as important as known reactivity.Lower separation points can provide for removal of a much greaterpercentage of hard burned lime from the soft burned fraction, but willoften sacrifice lime that may be sufficiently soft burned to still beuseable for certain applications. Thus, the specific cut-off line fordivision of soft and hard burned (fine and coarse) fractions willgenerally be a matter of design choice depending on the specificapplication and process to which the lime is to be put. However, theseparation point will generally be between the two peaks.

Depending on embodiment, the fractions may be separated by either of twomethods. In the first method, a particular size particle is used as acut-off between the fractions. Thus, the coarse fraction could bedefined as being all the particles larger than a particular size, forexample, larger than about 4 to about 7 microns. Again, it should berecognized that the indicated size is merely exemplary and any size maybe used as the cut-off. Alternatively, instead of selecting a particularsize cut off into which to divide the particulate into the twofractions, the fractions may instead be selected based on a percentageratio. Thus, instead of selecting to separate the particle distributionsinto two distributions based on a particular cutoff size, the fractionsmay instead be separated by removing a finest (or coarsest) fixedpercentage. In particular, the percentage cutoff may be chosen where thefine fraction is selected to be the finest 10%, 20%, 25%, 30% or anyother amount of the raw product. This type of arrangement, however, canbe problematic in that the location of the “middle fraction” may moveand certain batches may still be more reactive than others.

In the classification of the distribution of a raw quicklime output fromthe kiln as shown in the FIGS. such a percentage separation was used. Inparticular, the smallest about 20% of the distribution was removed asthe fine fraction and the remaining about 80% was used as the coarsefraction. The raw quicklime prior to classification is shown in FIG. 1 .As should be apparent, the distribution is quite wide. The coarsefraction's distribution is shown in FIG. 2 and it should be apparentthat there are still particles down to the minimum sizes detected inFIG. 1 . However, the majority of the particles have become larger andthe fine tail is much smaller. Similarly, FIG. 3 shows the fine fractionwhich is smaller and softer burned high reactive lime. Again, there isstill a distribution of particles, but the distribution of the fineportion of FIG. 3 shows a much more classic normal distribution (bellcurve) than was present in either of the other two distributions.

The specific distributions within the fine and coarse fractions willgenerally depend on the method of classification. In the embodiment ofFIGS. 1-3 , the two fractions were selected by removing the fine portionfrom the coarse portion via air classification (turbine classifier).This would commonly be used if the fine portion was considered the morevaluable, or the one that had more demanding requirements. By selectingthis as the controlled fraction (the one which is detected and removedfrom the other) the fine fraction generally has the coarse particles cutout, while the coarse fraction may still have a few finer particles.Specifically, the classification in this case is concerned that the fineportion not include coarse particles and reduces their presence byallowing the coarse portion to have some fine particles. In alternativeembodiments, the reverse could be true and the coarse portion could becontrolled, providing that the coarse fraction have fewer fine particlesat the expense of the fine portion having some coarser particles.

In a further embodiment, if a middle fraction was desired, the middlefraction could be determined by first removing the finest fraction fromthe coarse and setting this aside. The coarse fraction could then beclassified to remove the coarsest portion and that can be set aside. Theremaining middle portion will generally include some of the finerportion (and some of the coarser) but will generally be expected to beprimarily focused in the medium burned area.

FIG. 4 shows that, with the use of an air classification system and themethods described herein, the soft burned lime fraction was quitesuccessfully separated from the remainder of the kiln discharge.Specifically, with an about 20% cut ratio, the BET surface area of thefine fraction was essentially double that of the coarse fraction (andquite a bit higher than the raw feed as a whole too), and the BET porevolume of the fine fraction was also more than double that of the coarsefraction (and also significantly higher than the raw feed). Thus, thefine fraction is much more highly reactive than the coarse fraction andmore highly reactive than the discharge as a whole, and the finefraction will include a much higher percentage of softer burned limewhile the coarse fraction includes a much higher percentage of hardburned lime.

The connection with the size and the burn level is abundantly clear inFIG. 4 . In FIG. 4 , it can be seen that when the raw material, as wellas each fraction separately, were slaked with water, they displayed verydifferent reactivity. The fine fraction of FIG. 3 slaked significantlyfaster and better than either the raw feed and the coarse faction (whichwas clearly the slowest). As can be seen in the legend of FIG. 4 , basedupon the general classification of soft and hard burning particles basedon slaking characteristics (e.g., R30 and R180), the fine fraction isclearly classified with a majority well into a soft burn particulate,while the coarse fraction has a majority well into a hard burnparticulate.

As there are industries that desire a harder burned lime (e.g.,petroleum additives) with a smaller soft burn fraction and others thatdesire only a softer burned fraction (e.g., for generating slaked lime),by using this system and method of classification refinement, bothclassified fractions are of greater value than the original feed to theappropriate industry as each fraction displays an increased percentageof the appropriate lime (soft or hard burned). It should now also beapparent that by changing the cut ratio (or the cut-off size) betweenthe coarse and fine material (and by potentially adding an additional,or more, cut-off to separate middle fractions), the producer gainscontrol over the specific reactivity and can actually provide a materialwith a selected BET surface area, BET pore volume, or any other specificphysical characteristic based on the specifics of the industry orreaction which will use the quicklime.

While the invention has been disclosed in conjunction with a descriptionof certain embodiments, including those that are currently believed tobe the preferred embodiments, the detailed description is intended to beillustrative and should not be understood to limit the scope of thepresent disclosure. As would be understood by one of ordinary skill inthe art, embodiments other than those described in detail herein areencompassed by the present invention. Modifications and variations ofthe described embodiments may be made without departing from the spiritand scope of the invention.

It will further be understood that any of the ranges, values,properties, or characteristics given for any single component of thepresent disclosure can be used interchangeably with any ranges, values,properties, or characteristics given for any of the other components ofthe disclosure, where compatible, to form an embodiment having definedvalues for each of the components, as given herein throughout. Further,ranges provided for a genus or a category can also be applied to specieswithin the genus or members of the category unless otherwise noted.

The invention claimed is:
 1. A method for separating soft-burnedquicklime from hard-burned quicklime, the method comprising: providing aquicklime particulate with a particle size smaller than 100 mesh, thequicklime particulate having a size distribution with two peaks in abimodal distribution; and running said quicklime particles through aclassifier to separate said quicklime particles into a soft burned and ahard burned fraction separated by a dividing point, said soft burnedfraction being particles smaller than said dividing point and said hardburned fraction being particles larger than said dividing point; whereinsaid dividing point is between said two peaks in said bimodaldistribution.
 2. The method of claim 1 wherein said dividing point isdefined by a specific particle size.
 3. The method of claim 2 whereinsaid dividing point is selected to be between 4 and 7 microns.
 4. Themethod of claim 1 wherein said dividing point is defined as a size underwhich a percentage of particles in said remainder is below.
 5. Themethod of claim 4 wherein said percentage is about 20%.
 6. The method ofclaim 1 wherein said soft burned fraction has an R180 of greater than 40degrees.
 7. The method of claim 6 wherein said hard burned fraction hasan R180 of less than 30 degrees.
 8. The method of claim 1 furthercomprising: selecting a second dividing point; and removing from saidsoft burned fraction a medium burned fraction, said medium burnedfraction being particles larger than said second dividing point.
 9. Themethod of claim 8 wherein said soft burned fraction has an R180 ofgreater than 40 degrees, said medium burned fraction has an R180 between30 and 40 degrees, and said hard burned fraction has an R180 of lessthan 30 degrees.
 10. The method of claim 1 further comprising: selectinga second dividing point; and removing from said hard burned fraction amedium burned fraction, said medium burned fraction being particlessmaller than said second dividing point.
 11. The method of claim 10wherein said soft burned fraction has an R180 of greater than 40degrees, said medium burned fraction has an R180 between 30 and 40degrees, and said hard burned fraction has an R180 of less than 30degrees.
 12. A system for separating soft-burned quicklime fromhard-burned quicklime, the system comprising: a quicklime particulatewith a particle size smaller than 100 mesh, the quicklime particulatehaving a size distribution with two peaks in a bimodal distribution; andmeans for separating said quicklime particles into a soft burned and ahard burned fraction separated by a dividing point, said soft burnedfraction being particles smaller than said dividing point and said hardburned fraction being particles larger than said dividing point; whereinsaid dividing point is between said two peaks in said bimodaldistribution; wherein said soft burned fraction has an R180 of greaterthan 40 degrees; and wherein said hard burned fraction has an R180 ofless than 30 degrees.
 13. The system of claim 12 wherein said dividingpoint is defined by a specific particle size.
 14. The system of claim 13wherein said dividing point is selected to be between 4 and 7 microns.15. The system of claim 12 wherein said dividing point is defined as asize under which a percentage of particles in said remainder is below.16. The system of claim 15 wherein said percentage is about 20%.